454 AN INTRODUCTION TO CHILD STUDY

ment equivalent to about eight months between the children
of the upper social classes and those of the lower social
classes. A ten-year-old child who in early childhood has
acquired incorrect habits of speech which are inappropriate
for his present environment is definitely handicapped. One
intelligent youngster developed two languages, one for use
in school and the other for use at home and on the street.
In school he was marked A in oral English at the very time
he was using such expressions as "I ain't got nothin' " out of
school. Habits of wrong grammar and, to an even greater
extent, habits of incorrect articulation are extremely diffi-
cult to eradicate once they have been firmly established.
The age of a child's associates likewise is related to his
language development. In this respect younger children
have an advantage. They gain a great deal from their con-
versations with older brothers and sisters whose language
is in advance of theirs, but not too far above their level.
Twins, lacking this stimulation, tend to be relatively re-
tarded in language development. Occasionally, they fail
to acquire adult language because they have developed a
secret language which meets most of their social needs. Asso-
ciation with cultured adults is an important factor in the
language development of older children.
The study of a child's language throws light on his total
personality. The purpose for which he uses language —
whether to attain social ends, or merely to communfcate,
or to express personal power, or to display his knowledge
or self-importance is significant. The scope and precision
of his verbal expression indicates his habits of thought. The
answers he makes to questions and his spontaneous remarks
give adults an idea of the way the world appears to him.
Thus, language reveals the personality to a remarkable
extent.
Growth of Vocabulary. — During these preadolescent
years the child's vocabulary should grow in size, vividness,
and precision. It has been estimated that six-year-old chil-
dren, on the average, have a vocabulary of approximately
2,500 words. The vocabulary estimated from the Binet test